National Geographic : 1892 Mar 21
The Glacier's Snout. edly reach deep water. The Taku glacier, close by, finds no such support at the opening of its gorge, and therefore discharges into the water as a tide-water glacier. Davidson glacier, Lynn canal, has a termination exactly like that of the Norris. The great Malaspina glacier seems to be merely the united ends of the many large glaciers flowing from the St. Elias alps, expanded on the great plateau which borders these mountains on the south.* Tide-water Glaciers.-The Muir glacier is an excellent ex ample of this class. The inlet into which it pours increases in depth from the sides to not less than 720 feet near the middle; but the ice is so thick that even this depth is not sufficient to float it. Here we have an entirely different method of waste. The ice breaks off and floats away' in the water as icebergs. What is it that regulates the rate at which the ice breaks off? What is the form of the glacier's end below the water ? Above, it is practically vertical. I can only give a partial answer to these questions. Suppose the end of Muir glacier were vertical from top to bot tom; let us apply what we know of the motion of glaciers to this case and see what would follow. The more rapid motion of the upper part would result in its projection beyond the lower part, and this would become greater and greater until its weight was sufficient in itself to break it off. The extent of the projec tion before a break would occur depends evidently on the strength of ice. The water supports the ice by its buoyancy, so that the weight tending to cause fracture is slightly less than the weight of that portion of the ice which is above water. The line of fracture is determined by the position of some crevasse or some irregular melting below the surface. This form seems to be one of stable equilibrium, for if the ice should project too far it would break off, and if it did not project far enough no break would occur until its proper motion had carried it out further. That the ice for several hundred feet below the surface does not in general project further than that above is evident from the fact that I have frequently seen large masses, extending to the very top of the ice-front, shear off and sink vertically into the water, disappear for some seconds, and then rise again almost to their original height before turning over. If there were any projection within 300 feet of the surface, this mass would have struck it and *See Russell, Exp. to Mount St. Elias: Nat: Geog. Mag., vol. iii, 1891, p. 121.
1892 May 15
1892 Feb 19